1. Field of the Invention
The present invention relates to a liquid crystal display device for guiding light from a backlight source to a light transmission member and irradiating a liquid crystal panel, and more specifically, to the improvement of the brightness of the liquid crystal panel.
2. Description of the Related Art
As shown in FIG. 11, a conventional ordinary liquid crystal display device is arranged such that: successively laminated on the back surface of a liquid crystal panel 31 are a protection/diffusion sheet 32; two lens sheets 33 disposed under the protection/diffusion sheet 32 for improving the brightness of light; a diffusion plate 34 disposed under the lens sheets 33 for diffusing the light; a light transmission member 35 composed of an acryl resin or the like and disposed below diffusion plate 34, a light transmission member reflection pattern 35b formed on the bottom surface of the light transmission member 35 by silk print or when the light transmission member is molded for reflecting the light upward; and a reflection sheet 36 disposed under the light transmission member 35 for reflecting the light upward. Further, a backlight source 38 composed of a cold cathode fluorescent lamp (CCFL) or the like is disposed in a lamp holder 37 on the one end surface 35a of the light transmission member 35 and a U-shaped reflection film 39 is held in the lamp holder 37 on the upper, lower and back sides of the backlight source 38 to reflect the light from the backlight source 38 forward.
The above respective components are held by an upper holder 40 and a lower holder 41 as a frame member.
The light from the backlight source 38 and the light reflected at the reflection film 39 are irradiated to the one end surface 35a of the light transmission member 35 positioned forward of the backlight source 38 and the light from the end surface 35a is entered into the light transmission member 35. Then, the incoming light can reach every point in the light transmission member 35 while irregularly reflecting therein.
The incoming light which irregularly reflects in the light transmission member 35 is reflected at the light transmission member reflection pattern 35b on the bottom surface of the light transmission member 35, the reflection sheet 36 under the light transmission member 35 and so on in an approximately vertical direction and emerges from the upper surface of the light transmission member 35.
At the time, the light from the backlight source 38 also emerges from the upper surface of the of the portion of the light transmission member 35 which is located on the other end surface (not shown) side thereof which is apart from the backlight source 38.
The light emerged from the upper surface of the light transmission member 35 is caused to pass through the diffusion plate 34, the lens sheets 33, the protection/diffusion sheet 32 on the lens sheets 33 and so on so that it can irradiate the effective display area 31a of the liquid crystal panel 31 from the backside thereof.
In the liquid crystal display device described above, however, the light which irradiates the liquid crystal panel 31 includes two kinds of light beams. One of the light beams, that is, a first light beam is such that when the light which emerges from the backlight source 38 and the reflection film 39 and travels straight in an approximately horizontal direction enters the light transmission member 35, the light irregularly reflects in the light transmission member 35 and the thus irregularly reflected light is reflected at the light transmission member reflection pattern 35b on the bottom surface of the light transmission member 35, the reflection sheet 36 under the light transmission member 35 and so on while changing its direction approximately perpendicularly to the light transmission member 35, then emerges upward from the upper surface of the light transmission member 35 and irradiates the entire surface of the effective display area 31a of the liquid crystal panel 31 from the backside thereof.
Whereas, the other of the light beams, that is, a second light beam is such that when an oblique light beam A shown by the arrow in FIG. 11 emerges from the backlight source 38 and the reflection film 39 obliquely upward with respect to the end surface 35a of the light transmission member 35 and enters the light transmission member 35, the oblique light beam A passes through the light transmission member 35 straight in an obliquely upward direction without irregularly reflecting in it, emerges from the light transmission member 35 and irradiates, in addition to the first light beam, the portion of the effective display area 31a which is shown in the schematic plan view of the liquid crystal display device in FIG. 12 and located near to the edge 31b thereof in the vicinity of the backlight source 38, for example, the portion of the effective display area 31a within the range of 10 mm from the edge 31b of the liquid crystal panel 31.
Since the portion of the effective display area 31a within the range of 10 mm from the edge 31b of the liquid crystal panel 31 is irradiated by the composite light beam composed of both the first and second light beams, the above portion of the effective display area 31a is brighter than the other portion thereof and "glittering state" emission lines 31c are generated. Accordingly, there is a problem that the brightness of the effective display area 31a of the liquid crystal panel 31 is made uneven.
As a coutermeasure to cope with the above problem, the conventional liquid crystal display device has a black or gray colored portion 36a formed thereto by print or the like within the range of approximately 10 mm, which is near to the backlight source 38, of the reflecting surface of the reflection sheet 36 under the light transmission member 35 to absorb a part of the first light beam so that the generation of the emission lines 1c is prevented by lowering the brightness of the effective display area 31a within the range of approximately 10 mm thereof near to the edge 31b.
In the conventional liquid crystal display device, however, since the "glittering state" emission lines 31c which are generated to the effective display area 31a of the liquid crystal panel 31 are prevented by the provision of the black or gray colored portion 36a formed within the range of approximately 10 mm near to the backlight source 38 of the reflection sheet 36, there is a problem that the surface brightness in the liquid crystal display area is lowered, although there is an effect that the light of the backlight source 38 is partly absorbed by the colored portion 36a and the quantity of light emerged upward from the light transmission member 35 is reduced and the generation of the emission lines is prevented.
As shown in FIGS. 13 and 14, another conventional liquid crystal display device has a reflector 59 whose interior is formed to a U-shape so as to encase a backlight source 38.
A reflecting surface 59b to which glossy processing is applied is formed to the interior of the opening 59a of the reflector 59 so that the reflecting surface 59b reflects the light irradiated from the backlight source 38 forward and irradiates the end surface 55a of a light transmission member 55.
Further, a case portion 59c on which the aforesaid respective components are placed is formed to the reflector 59 integrally therewith. The respective members are held by the reflector 59 having the case portion 59c and an upper holder 40 acting as a frame member.
According to the liquid crystal display device arranged as described above, in the liquid crystal panel 31 shown in FIG. 12 which shows the schematic plan view of the liquid crystal display device, there is a second light beam, that is, a reflected light beam C1 which irradiates, in addition to the above first light beam, the portion of the effective display area 31a of the liquid crystal panel 31 which is located near to the edge portion 31b in the vicinity of the backlight source 38, for example, the portion of the effective display area 31a of the liquid crystal panel 31 within the range of 10 mm from the edge 31b.
The behavior of second light beam or the reflected light beam C1 is such that since the above portion of the effective display area 31a is located near to the backlight source 38, when an oblique light beam C shown by the arrow in FIG. 13 irradiates the surface of a reflection sheet 56 within the range of 10 mm from the end surface 56a thereof, it is reflected at the reflection sheet 56 and the thus reflected light beam C1 passes through the light transmission member 55 straight in an obliquely upward direction without irregularly reflecting therein and emerges from the upper surface of the light transmission member 55 so as to irradiate the portion of the effective display area 31a within the range of 10 mm from the edge portion 31b of the liquid crystal panel 31.
The second light beam includes, in addition to the reflected light beam C1, a reflected light beam D1 which irradiates the portion the effective display area 31a within 10 mm from the edge 31b of the liquid crystal panel 31. The behavior of the reflected light beam D1 is such that when an oblique light beam D irradiates the lower plane portion 59d of the reflecting surface 59b of the reflector 59, in which the backlight source 38 is encased, on the side thereof near to the light transmission member 55, the oblique light beam D is reflected upward at the lower plane portion 59d and when the thus reflected light beam D1 enters the light transmission member 55 from the end surface 55a, it passes through the light transmission member 55 likewise the reflected light beam C1 and emerges from the upper surface of the light transmission member 55 so as to irradiate the portion of the effective display area 31a within the range of 10 mm from the edge portion 31b of the liquid crystal panel 31.
As a result, since the portion of the effective display area 31a within the range of 10 mm from the edge 31b of the liquid crystal panel 31 is irradiated by the composite light beam composed of the first and second light beams, the portion is made brighter than the other area. Thus, there is a problem that the brightness of the effective display area 31a of the liquid crystal panel 31 is made uneven by the generation of "glittering state" emission lines 31c.
As a coutermeasure to cope with the above problem, the conventional liquid crystal display device has a light quantity control portion 56b of, for example, black or gray formed by print or the like to the reflection sheet 56 under the light transmission member 55 within the range of 10 mm from the end surface 56a thereof for partly absorbing the second light beam so that the generation of the emission lines 1c is prevented by lowering the brightness of the effective display area 31a of the liquid crystal panel 3l within the range of approximately 10 mm thereof which is located near to the edge 31b as shown in FIG. 14.
In the aforesaid conventional liquid crystal display device, since the light quantity control portion 56b composed of the colored portion of for example, black or gray is formed by print or the like to the reflection sheet 56 within the range of 10 mm from the end surface 56a thereof as shown in FIG. 14 to absorb the oblique light beams from the backlight source 38, the reflected light beam C1 resulting from the oblique light C can be absorbed. However, since the oblique light beam D irradiating the lower plane portion 59d of the reflecting surface 59b is not absorbed, it emerges as the reflected light beam D1. Thus, there is caused a problem that since the brightness of the effective display area 31a of the liquid crystal panel 31 is made uneven and the emission lines 31c are generated and accordingly it is difficult to discriminate characters etc. displayed on the effective display area 31a.